Rabies virus (RV) is a non-segmented negative-stranded RNA virus of the Rhabdoviridae family and induces a fatal neurological disease in humans and animals. More than 70,000 human fatalities are reported annually and millions of others require post-exposure treatment. Although significant advances have been made in rabies prevention and control, the disease remains a major threat to public health and continues to cause numerous human deaths around the world. Canines remain the most important reservoir in Asia, Africa and Latin America where most human rabies cases occur. In the developed countries, human rabies has declined significantly during the past 50 years, primarily as a result of routine vaccination of pet animals. However, rabies transmission via exposure to wild-life has emerged as a major cause of the disease. In the United States, more than 90% of animal rabies cases have been reported in wildlife, representing continual public health threats. Most human cases in the past decade have been associated with RV found in bats, particularly silver-haired bats.
Rhabdoviruses have two major structural components: a helical ribonucleoprotein core (RNP) and a surrounding envelope. The rabies genome encodes five proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and polymerase (large protein) (L). The order of the genes in the wild-type rabies genome is 3′-N-P-M-G-L-5′. The N, L and P proteins are associated with the core RNP complex. The RNP complex consists of the RNA genome encapsidated by the N in combination with polymerase L and the P protein. This complex serves as a template for virus transcription and replication. The viral envelope component of RV is composed of a transmembrane glycoprotein (G) and a matrix (M) protein. The glycoprotein forms approximately 400 trimeric spikes which are tightly arranged on the surface of the virus. The M protein is associated both with the envelope and the RNP and may be the central protein of rhabdovirus assembly.
As noted above, rabies remains a major public health threat around the world. Controlling rabies and protecting humans from rabies requires several control strategies, such as routine immunization of pet animals and wildlife carriers, pre-exposure immunization of people at risk, and post-exposure treatment of people bitten by rabid animals. Although inactivated rabies virus (RV) vaccines prepared from cell culture are safe and well-tolerated, they have multiple disadvantages. They are difficult to manufacture, difficult to store, have low immunogenicity, and require multiple injections. Moreover, they are expensive and thus beyond the reach of most people who need the vaccines in the developing countries. In addition, these inactivated vaccines typically include adjuvants which may cause unwanted side effects. Thus, safer, cheaper, and more efficacious RV vaccines are needed.
The present application addresses this need through the development of a novel method for the production of virus-like particles (VLPs) comprising the rabies glycoprotein (G).